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Engine bolt torque setting

chris mitchell

Well Known Member
This question may be silly, but I cannot find clear definite information, tho it may be because I am belng slow....

So I have the four engine bolts installed and tightened up so that the mounts are bottomed out. The instructions say "tighten to standard AN7 values." Its a UNF thread, 20 turns per inch, so the standard value would be 450 to 500 inch pounds - considerably more than the "bottoming out" torque?

I notice on the "illustrated guide to engine hanging that it is suggested that the bolts are close tolerance - but I don't think they are?

Have I understood the torque instructions correctly?

Many thanks,

Chris
 
Bolt

They are bottomed out, you accomplish nothing with a torque wrench. Tighten until bottomed out. If they still turn they are not bottomed out.
 
Bolt

They are bottomed out, you accomplish nothing with a torque wrench. Tighten until bottomed out. Do not stretch the bolt.
 
I followed the instructions ... bottom out and torque to AN7 values; 40 foot pounds-ish. Then adjust the nut so you can put in the cotter pin.
 
Which engine bolts are you talking about? When you say "bottomed out" do you mean they have hit the bottom of their hole or do you mean they are tight against their washer?
 
I?m talking about the bolts that secure the engine to the mount, NOT the ones that hold the mount to the airframe.

As you tighten the bolts down, the rubber compressed and after a few turns I can feel the spacer within the mount come up against the J221861 washer at one end and the engine case at the other (top bolts). On the lower mounts the spacer is lodged between the J221861 and the AN970-7 at the other, as I understand the diagrams. At that point the rubber mount has bottomed out. You then further tighten to 450-500 inch pounds to apply appropriate torque/tightness for an AN7 bolt. As I understand the process.... is that correct??

Thanks and apologies if I?m being dumb!?

Chris
 
As far as I remember you are correct, it has been a while since I did this. The only thing I might say is that after you torque the bolts you will probably need to back off a little to get the cotter pin holes lined up and this kind of messes up that torque job you worried about getting perfect.
 
When torquing a castle nut, use the lower figure of the torque range, then tighten slightly as required to align the cotter pin hole. No backing off necessary.
 
When torquing a castle nut, use the lower figure of the torque range, then tighten slightly as required to align the cotter pin hole. No backing off necessary.

And was always taught to approach torque values from the lower end, never the upper. If you can't get them to line up within the spec, try again with different washers or combination of washer thicknesses, or try a different nut, or bolt, or both, or all three.
 
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